| 摘要 | 氧化亚氮(N2O)是大气中的重要温室气体，农业土壤排放是N2O的主要来源，其排放量占人为源的52%。土壤N2O排放不仅浪费肥料资源，降低肥料利用率，更主要的是与全球变暖和臭氧层破坏相关联。本研究以澳大利亚维多利亚州Rutherglen旱作小麦田和新维尔士州Griffith灌溉玉米地为研究对象，通过室内培养、田间试验和模型预测相结合的方法，研究了土壤水分、温度、有效C浓度、有效N浓度等主要因素对土壤硝化、反硝化反应中N2O排放的影响,田间土壤N2O排放时空变异及其机理，在此基础上对减缓土壤N2O排放的措施进行了有效探索，提出了减少土壤N2O排放的技术措施及适用条件，为预测及减缓土壤N2O排放、合理N素管理提供了理论依据。取得的主要结论如下：1.土壤硝化反应速度及反应中N2O排放主要受土壤温度、水分、NH4+浓度的影响。Rutherglen旱地小麦田土壤潜在的硝化反应最大速度为6.67mg/kg·d,硝化反应中N2O最大排放比例为3.03%；随温度由10 oC升高30 oC，硝化反应速度指数升高,N2O排放总量增加，但N2O排放比例明显降低；NH4+浓度升高可抑制硝化反应的进行，提高硝化反应中N2O排放比例。随水分含量由20%WFPS升高到40%WFPS时硝化反应速度增加到最大，60%WFPS时略有降低。Griffith灌溉玉米地土壤硝化反应发生的适宜温度为10oC-20oC，适宜水分为40%WFPS-60%WFPS，30oC、20%WFPS时硝化反应速度明显受到抑制。适宜条件下，灌溉玉米地土壤硝化反应速度高于旱地小麦田，反应中N2O排放比例低于旱地小麦田。2.土壤反硝化反应对N2O排放的贡献受土壤水分含量、有效N浓度、有效C浓度及其交互作用的影响。水分含量由65%WFPS升高到80%WFPS时N2O排放急剧增加。50%WFPS－95%WFPS范围内，反硝化均是N2O产生的主要过程，且随水分含量的增加，反硝化对N2O排放的贡献率增加。有效N浓度增加可显著增加N2O总排放量,反硝化对N2O排放的贡献率及反硝化反应中N2O排放量。有效C对N2O排放的影响与水分含量和有效N浓度有关,加入外源N的基础上,外源C的加入可提高反硝化对N2O排放的贡献率及反硝化中N2O排放量。3.土壤水分变化和施肥、土壤N转化引起的NH4+/NO3-含量变异是田间土壤N2O排放时空变异的主要原因。Rutherglen旱地小麦田肥料N总损失为2.7%－12.7%，N2O气态损失为0.085%-0.097%，远低于IPCC使用的N2O排放系数（1.25%）；水分含量和NO3-含量都较适宜的6月和次年2月是N2O排放的二个高峰期。Griffith灌溉玉米地高温高湿的土壤环境促进了土壤反硝化损失和N2O排放, 肥料N总损失为31.5%－36.5%，其中反硝化损失11.7%-11.9%；N2O气态损失0.47%－1.90%, N肥用量增加使N2O排放量及N2O排放系数增加，土壤N2O主要从垄坡中部的施肥点附近排出。4.WNMM可较好地模拟旱地小麦田土壤水分、NH4+、NO3-的动态，亦可较好地模拟N2O的排放动态，但在土壤水分、温度变化幅度较大的9月10日－10月10日模拟的N2O排放显著大于测定值，还需要对WNMM模型中土壤N2O排放的模拟过程进行修正，提高N2O排放预测的可靠性。5.提出了运用硝化抑制剂（N-Serve）、通气调节和秸秆还田减缓土壤N2O排放的技术措施及适用条件。硝化抑制剂主要是抑制硝化反应及硝化反应中N2O排放,应优先用于低水分含量土壤；土壤掺砂、通气调节可有效地抑制反硝化及反硝化中N2O排放，主要适用于质地粘重，高水分含量土壤；秸秆直接还田的主要作用在于影响了土壤的C、N循环，从而影响了土壤反硝化及N2O排放,其对N2O排放的影响作用与N肥用量有关，建议在高施肥量或低水分含量条件下运用。 |
| 其他摘要 | Nitrous oxide (N2O) is an important greenhouse gas involved in the catalytic destruction of the ozone layer. Agricultural soils emission of N2O is the major sources that contribute to 52% of the total N2O due to human being activity. N2O emission from the soils not only wastes fertilizer resources, reducing nitrogen fertilizer efficiency, what is more, that is related with global warming and the destruction of the ozone layer. In this paper, laboratory incubation, field measurement and simulation method were applied to investigate effects of the main environmental factors, such as soil moisture, temperature, the concentration of available carbon and available nitrogen on the N2O emitted from rain-fed wheat soil in Rutherglen, Victoria, and irrigated maize soil in Griffith, New South Wales, Australia, and temporary and spatial variability of N2O emission in the field and its mechanism. In addition, several methods of reducing N2O emission from soil and applicability were pointed out on the basis of the present study. This will provide a theoretical foundation for predicting and reducing soil N2O emission, management of nitrogen fertilizer. The present study have obtained following results: 1. Soil nitrification rate and N2O emission from nitrification is mainly controlled by soil temperature, soil moisture and NH4+-N concentration. The potential maximum nitrification rate is 6.67mg/kg·d for the Rutherglen rain-fed wheat soil, and potential maximum N2O emission fraction is 3.03%. Nitrification rate increased exponentially, and the total N2O emission also increased, but N2O fraction decreases significantly when the temperature increased from 10oC to 30oC. Increasing NH4+-N concentration in the soil inhibited the nitrification process, on the other hand, N2O emission fraction were increased. Soil nitrification rate increases with the increase of soil moisture from 20 to 40%WEPS, and reaches its peak at 40%WFPS, then declines with soil moisture increased to 60%WFPS. The optimal temperature for soil nitrification process is 10oC -20oC for the Griffith soil, and the optimal moisture is from 40 to 60%WFPS. Soil nitrification process is inhibited significantly under the temperature at 30oC and soil moisture at 20%WFPS. Compared with the rain-fed soil, nitrification rate of the irrigated soil is higher and N2O emission fraction from nitrification is lower.2. The contribution of denitrification to N2O emission is influenced by soil moisture, concentrations of available nitrogen, available carbon and the interaction of these factors. N2O emission increases sharply with soil moisture increased to 80%WFPS. Most of the N2O is emitted from denitirification when soil moisture is in the range from 50% to 95%WFPS, and the contribution of denitrification to N2O emission increased with soil moisture increasing. Total N2O emission, contribution of denitrification and N2O emitted from denitrification increased with the increase of available N concentration. The effect of available carbon on N2O emission is related with soil moisture and nitrogen concentration. The addition of C, in combination with nitrogen amendment, increased the contribution of denitrification and N2O emission from denitrification. 3. The variation of soil moisture and NH4+/NO3- concentration due to fertilization and nitrogen transformation is the main reason of the temporary and spatial variability of N2O emission in the field. In the Rutherglen rain-fed wheat ecosystem, the total nitrogen fertilizer loss is from 2.7% to 12.7%, N2O emission in form of gas is 0.085%-0.097%, which is much lower than that used by IPCC(1.25%). Two N2O emission peaks exist in the yearly experimental period, one is June, 2004, and the other is February, 2005, during that period suitable soil moisture is combined with suitable nitrate concentration. In the Griffith irrigated maize ecosystem, high soil temperature and moisture enhance soil denitrification and N2O emission, total nitrogen fertilizer loss is 31.5%－36.5%, in which 11.7%-11.9% results from denitrification. N2O emission in form of gas is 0.47%-1.9%. Total N2O emission and N2O emission factor increase with the increase of fertilization rate, with most of N2O was emitted from the bed shoulder, from where fertilizer was applied into the soil.4. WNMM model well simulates soil moisture, NH4+, NO3- of the rain-fed wheat soil, also gives a satisfactory prediction of N2O fluxes. However, the predicted N2O flux is much higher than the measured from 10, September to 10, October, 2004, when soil moisture and temperature had a drastic fluctuation, it is necessary to modify N2O prediction gas module.5. It is suggested N2O emission mitigation by using nitrification inhibitor (N-Serve), regulating soil aeration and incorporating stubble into soil and applicability of all these techniques. The main effect of nitrification inhibitor is reducing N2O emission from nitrification by inhibiting soil nitrification, it should be first used in low soil moisture condition. Regulating soil aeration by adding sand is more suitable in clay and high moisture soil in that it is very efficient in inhibiting denitrification, decreasing N2O emission from denitrification. The effect of stubble incorporation on N2O emission is related with soil nitrogen fertilization rate by influencing soil C and N transformation, it is recommended to apply when fertilization rate is high or soil moisture is low. |
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